pineal gland

A small, cone-shaped endocrine gland,
also called the pineal body or epiphysis cerebri.
The pineal gland extends posteriorly from the third ventricle of the brain.
It consists of portions of neurons, neuroglial
cells, and specialized secretory cells called pinealocytes.
The pinealocytes synthesize the hormone melatonin
and secrete it directly into the cerebrospinal
fluid, which takes it into the blood. Melatonin affects reproductive
development and daily physiologic cycles.

Calcium deposition in the pineal makes it a useful marker of midline in
skull X-rays.